1. Field of the Invention
This invention relates to apparatus for selectively forming a continuously moving web with apertures or holes by means of a punching mechanism consisting of a rotating die and a rotating punch and with venting pinholes by means of a rotating needle bar and a rotating abutment.
2. Description of the Prior Art
For instance, in machines for making continuous tubular films from flat webs of synthetic thermoplastics, which continuous tubular films are subsequently severed to form tubing sections for making sacks or bags, it is desired to form venting pinholes or thumbholes in the flat starting web which has not yet been folded to form a tubing. Such punched thumbholes are desired to ensure that a sack which has been closed at one end can be more easily opened at its open end.
In known machines for punching thumbholes or for forming venting pinholes, a shaft was provided at its center with a tool for punching thumbholes and was provided with needle bars on both sides of said tool. If sacks closed at both ends were to be made from the web when it has been folded to form a continuous tubing, only the needle bars for forming pinholes and the associated abutments were used whereas the thumbhole-punching mechanism consisting of a die and punch was disabled. When the web had been folded to form a tubing for use in making sacks which were closed only at one end and provided with an open edge at the other end, the means for forming pinholes were disabled and the thumbhole-punching mechanism was used to punch the desired thumbholes. Those known machines cannot be used to process rather narrow webs because the presence of the centrally disposed mechanism for punching thumbholes precludes the provision of the means for forming pinholes on opposite sides of said punching mechanism. In order to permit a selective forming of punched thumbholes or of venting pinholes, the corresponding punching and pinhole-forming mechanisms had to be arranged in succession and to be provided with separate drives. This involves a higher structural and mechanical expenditure and has the result that the machines have an undesirably large length.